High resistivity SOI wafers and a method of manufacturing thereof

ABSTRACT

A high resistivity single crystal semiconductor handle structure for use in the manufacture of SOI structure is provided. The handle structure comprises an intermediate semiconductor layer between the handle substrate and the buried oxide layer. The intermediate semiconductor layer comprises a polycrystalline, amorphous, nanocrystalline, or monocrystalline structure and comprises a material selected from the group consisting of Si1-xGex, Si1-xCx, Si1-x-yGexSny, Si1-x-y-zGexSnyCz, Ge1-xSnx, group IIIA-nitrides, semiconductor oxides, and any combination thereof.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 15/112,083, filed on Jul. 15, 2016, the disclosure of which ishereby incorporated by reference in its entirety. U.S. application Ser.No. 15/112,083 is a National Stage Application of InternationalApplication No. PCT/US2014/072546, filed on Dec. 29, 2014, thedisclosure of which is hereby incorporated by reference in its entirety.International Application No. PCT/US2014/072546 claims priority to U.S.Provisional Application Ser. No. 61/930,507, filed on Jan. 23, 2014, thedisclosure of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of semiconductorwafer manufacture. More specifically, the present invention relates to amethod for forming a semiconductor-on-insulator (e.g.,silicon-on-insulator) structure, and more particularly to a method forproducing a handle wafer that is resistant to formation of an inversionlayer in the region near the buried oxide layer, the handle wafer beinguseful in the manufacture of a semiconductor-on-insulator structure.

BACKGROUND OF THE INVENTION

Semiconductor wafers are generally prepared from a single crystal ingot(e.g., a silicon ingot) which is trimmed and ground to have one or moreflats or notches for proper orientation of the wafer in subsequentprocedures. The ingot is then sliced into individual wafers. Whilereference will be made herein to semiconductor wafers constructed fromsilicon, other materials may be used to prepare semiconductor wafers,such as germanium, silicon carbide, silicon germanium, or galliumarsenide.

Semiconductor wafers (e.g., silicon wafers) may be utilized in thepreparation of composite layer structures. A composite layer structure(e.g., a semiconductor-on-insulator, and more specifically, asilicon-on-insulator (SOI) structure) generally comprises a handle waferor layer, a device layer, and an insulating (i.e., dielectric) film(typically an oxide layer) between the handle layer and the devicelayer. Generally, the device layer is between about 0.01 micrometer andabout 20 micrometers thick, such as between about 0.05 micrometer and 20micrometers thick. In general, composite layer structures, such assilicon-on-insulator (SOI), silicon-on-sapphire (SOS), andsilicon-on-quartz, are produced by placing two wafers in intimatecontact, followed by a thermal treatment to strengthen the bond.

After thermal anneal, the bonded structure undergoes further processingto remove a substantial portion of the donor wafer to achieve layertransfer. For example, wafer thinning techniques, e.g., etching orgrinding, may be used, often referred to as back etch SOI (i.e., BESOI),wherein a silicon wafer is bound to the carrier wafer and then slowlyetched away until only a thin layer of silicon on the carrier waferremains. See, e.g., U.S. Pat. No. 5,189,500, the disclosure of which isincorporated herein by reference as if set forth in its entirety. Thismethod is time-consuming and costly, wastes one of the substrates andgenerally does not have suitable thickness uniformity for layers thinnerthan a few microns.

Another common method of achieving layer transfer utilizes a hydrogenimplant followed by thermally induced layer splitting. Particles (e.g.,hydrogen atoms or a combination of hydrogen and helium atoms) areimplanted at a specified depth beneath the front surface of the donorwafer. The implanted particles form a cleave plane in the donor wafer atthe specified depth at which they were implanted. The surface of thedonor wafer is cleaned to remove organic compounds deposited on thewafer during the implantation process.

The front surface of the donor wafer is then bonded to a carrier waferto form a bonded wafer through a hydrophilic bonding process. Prior tobonding, the donor wafer and/or carrier wafer are activated by exposingthe surfaces of the wafers to plasma containing, for example, oxygen ornitrogen. Exposure to the plasma modifies the structure of the surfacesin a process often referred to as surface activation, which activationprocess renders the surfaces of one or both of the donor water andcarrier wafer hydrophilic. The wafers are then pressed together and abond is formed there between. This bond is relatively weak, and must bestrengthened before further processing can occur.

In some processes, the hydrophilic bond between the donor wafer andcarrier wafer (i.e., a bonded wafer) is strengthened by heating orannealing the bonded wafer pair. In some processes, wafer bonding mayoccur at low temperatures, such as between approximately 300° C. and500° C. In some processes, wafer bonding may occur at high temperatures,such as between approximately 800° C. and 1100° C. The elevatedtemperatures cause the formation of covalent bonds between the adjoiningsurfaces of the donor wafer and the carrier wafer, thus solidifying thebond between the donor wafer and the carrier wafer. Concurrently withthe heating or annealing of the bonded wafer, the particles earlierimplanted in the donor wafer weaken the cleave plane.

A portion of the donor wafer is then separated (i.e., cleaved) along thecleave plane from the bonded wafer to form the SOI wafer. Cleaving maybe carried out by placing the bonded wafer in a fixture in whichmechanical force is applied perpendicular to the opposing sides of thebonded wafer in order to pull a portion of the donor wafer apart fromthe bonded wafer. According to some methods, suction cups are utilizedto apply the mechanical force. The separation of the portion of thedonor wafer is initiated by applying a mechanical wedge at the edge ofthe bonded wafer at the cleave plane in order to initiate propagation ofa crack along the cleave plane. The mechanical force applied by thesuction cups then pulls the portion of the donor wafer from the bondedwafer, thus forming an SOI wafer.

According to other methods, the bonded pair may instead be subjected toan elevated temperature over a period of time to separate the portion ofthe donor wafer from the bonded wafer. Exposure to the elevatedtemperature causes initiation and propagation of a crack along thecleave plane, thus separating a portion of the donor wafer. This methodallows for better uniformity of the transferred layer and allows recycleof the donor wafer, but typically requires heating the implanted andbonded pair to temperatures approaching 500° C.

The use of high resistivity semiconductor-on-insulator (e.g.,silicon-on-insulator) wafers for RF related devices such as antennaeswitches offers benefits over traditional substrates in terms of costand integration. To reduce parasitic power loss and minimize harmonicdistortion inherent when using conductive substrates for high frequencyapplications it is necessary, but not sufficient, to use substratewafers with a high resistivity. Accordingly, the resistivity of thehandle wafer for an RF device is at least 50 Ohm-cm, and more commonlygreater than about 500 Ohm-cm. A very high resistivity semiconductorsubstrate, such as a silicon wafer, is prone to formation of highconductivity charge inversion or accumulation layers at the BOX/handleinterface which reduce the effective resistivity of the substrate andgive rise to parasitic power losses and device nonlinearity when thedevices are operated at RF frequencies. See FIG. 1, which depicts a highresistivity silicon-on-insulator structure 1 comprising a P-type handlesubstrate 2, a buried oxide layer 4 having positive charges 6, and asilicon device layer 8. An N-type inversion layer 10 forms at theinterface of the buried oxide layer 4 having positive charge 6 and theP-type handle substrate 2. These inversion/accumulation layers 10 can bedue to BOX fixed charge, oxide trapped charge, interface trapped charge,and even DC bias applied to the devices themselves.

Methods have been developed to trap the charge in any induced inversionor accumulation layers so that the high resistivity of the substrate ismaintained even in the very near surface region. It is known that chargetrapping layers (CTL) between the high resistivity handle substrates andthe buried oxide (BOX) may improve the performance of RF devicesfabricated using SOI wafers. A number of methods have been suggested toform these high interface trap layers. For example, one of the method ofcreating a semiconductor-on-insulator (e.g., a silicon-on-insulator, orSOI) with a CTL for RF device applications is based on depositing anundoped polysilicon film on a silicon substrate having high resistivityand then forming a stack of oxide and top silicon layer on it. Apolycrystalline silicon layer acts as a high defectivity layer betweenthe silicon substrate and the buried oxide layer. See FIG. 2, whichdepicts a silicon-on-insulator structure 20 comprising high resistivitysubstrate 22, a buried oxide layer 24, and a silicon device layer 26. Atrap rich layer 28, for example, a polycrystalline silicon film, for useas a charge trapping layer between a high resistivity substrate 22 andthe buried oxide layer 24 in the silicon-on-insulator structure 20. Analternative method is the implantation of heavy ions to create a nearsurface damage layer. Devices, such as radiofrequency devices, are builtin the top silicon layer 26.

It has been shown in academic studies that the polysilicon layer inbetween of the oxide and substrate improves the device isolation,decreases transmission line losses, and reduces harmonic distortions.See, for example: H. S. Gamble, et al. “Low-loss CPW lines on surfacestabilized high resistivity silicon,” Microwave Guided Wave Lett.,9(10), pp. 395-397, 1999; D. Lederer, R. Lobet and J.-P. Raskin,“Enhanced high resistivity SOI wafers for RF applications,” IEEE Intl.SOI Conf., pp. 46-47, 2004; D. Lederer and J.-P. Raskin, “New substratepassivation method dedicated to high resistivity SOI wafer fabricationwith increased substrate resistivity,” IEEE Electron Device Letters,vol. 26, no. 11, pp. 805-807, 2005; D. Lederer, B. Aspar, C. Laghae andJ.-P. Raskin, “Performance of RF passive structures and SOI MOSFETstransferred on a passivated HR SOI substrate,” IEEE International SOIConference, pp. 29-30, 2006; and Daniel C. Kerr et al. “Identificationof RF harmonic distortion on Si substrates and its reduction using atrap-rich layer”, Silicon Monolithic Integrated Circuits in RF Systems,2008. SiRF 2008 (IEEE Topical Meeting), pp. 151-154, 2008. In practice,the effectiveness of a polycrystalline silicon layer as a chargetrapping layer may not be sufficient to meet the performance targets foradvanced SOI RF devices. In some cases, the CTL may degrade devicecharacteristics.

SUMMARY OF THE INVENTION

Briefly, the present invention is directed to a single crystalsemiconductor handle structure comprising: a single crystalsemiconductor handle substrate comprising two major, generally parallelsurfaces, one of which is a front surface of the single crystalsemiconductor handle substrate and the other of which is a back surfaceof the single crystal semiconductor handle substrate, a circumferentialedge joining the front and back surfaces of the single crystalsemiconductor handle substrate, and a central plane of the singlecrystal semiconductor handle substrate between the front and backsurfaces of the single crystal semiconductor handle substrate, whereinthe single crystal semiconductor handle substrate comprises a p-typedopant and has a minimum bulk resistivity of 50 Ohm-cm; an intermediatesemiconductor layer having electron affinity lower than that of thesingle crystal semiconductor handle substrate, wherein the intermediatesemiconductor layer comprises a polycrystalline, amorphous,nanocrystalline, or monocrystalline structure and comprising a materialselected from the group consisting of Si_(1-x)Ge_(x), Si_(1-x)C_(x),Si_(1-x-y)Ge_(x)Sn_(y), Si_(1-x-y-z)Ge_(x)Sn_(y)C_(z), Ge_(1-x)Sn_(x), agroup IIIA-nitride, a metal oxide, and any combination thereof whereinx, y, and z are molar ratios with values between 0 and 1; and asemiconductor oxide layer.

The present invention is further directed to a method of preparing asingle crystal semiconductor handle wafer in the manufacture of asemiconductor on insulator device, the single crystal semiconductorhandle wafer comprising two major, generally parallel surfaces, one ofwhich is the front surface of the single crystal semiconductor handlewafer and the other of which is a back surface of the single crystalsemiconductor handle wafer, a circumferential edge joining the front andback surfaces of the single crystal semiconductor handle wafer, a bulksingle crystal semiconductor region, and the central plane of the singlecrystal semiconductor handle wafer between the front and back surfacesof the single crystal semiconductor handle wafer, wherein the singlecrystal semiconductor handle wafer has a minimum bulk resistivity of atleast 50 Ohm-cm, the method comprising: forming an intermediatesemiconductor layer having electron affinity lower than that of thesingle crystal semiconductor handle substrate, wherein the intermediatesemiconductor layer comprises a polycrystalline, amorphous,nanocrystalline, or monocrystalline structure and comprising a materialselected from the group consisting of Si_(1-x)Ge_(x), Si_(1-x)C_(x),Si_(1-x-y)Ge_(x)Sn_(y), Si_(1-x-y-z)Ge_(x)Sn_(y)C_(z), Ge_(1-x)Sn_(x), agroup IIIA-nitride, a metal oxide, and any combination thereof whereinx, y, and z are molar ratios with values between 0 and 1; and forming asemiconductor oxide layer in interfacial contact with the intermediatesemiconductor layer.

The present invention is still further directed to a method of preparinga silicon-on-insulator structure, the method comprising: bonding anexposed front surface layer of a single crystal semiconductor handlestructure and an exposed oxidized front surface of a single crystalsilicon donor wafer; wherein the single crystal semiconductor handlestructure comprises (a) a single crystal semiconductor handle substratecomprising two major, generally parallel surfaces, one of which is afront surface of the single crystal semiconductor handle substrate andthe other of which is a back surface of the single crystal semiconductorhandle substrate, a circumferential edge joining the front and backsurfaces of the single crystal semiconductor handle substrate, and acentral plane of the single crystal semiconductor handle substratebetween the front and back surfaces of the single crystal semiconductorhandle substrate, wherein the single crystal semiconductor handlesubstrate comprises a p-type dopant and has a minimum bulk resistivityof 50 Ohm-cm; (b) an intermediate semiconductor layer having electronaffinity lower than that of the single crystal semiconductor handlesubstrate, wherein the intermediate semiconductor layer comprises apolycrystalline, amorphous, nanocrystalline, or monocrystallinestructure and comprising a material selected from the group consistingof Si_(1-x)Ge_(x), Si_(1-x)C_(x), Si_(1-x-y)Ge_(x)Sn_(y),Si_(1-x-y-z)Ge_(x)Sn_(y)C_(z), Ge_(1-x)Sn_(x), a group IIIA-nitride, ametal oxide, and any combination thereof wherein x, y, and z are molarratios with values between 0 and 1; and (c) a semiconductor oxide layer;and wherein the single crystal silicon donor wafer comprises two major,generally parallel surfaces, one of which is the exposed oxidized frontsurface of the single crystal silicon donor wafer and the other of whichis a back surface of the single crystal silicon donor wafer, acircumferential edge joining the front and back surfaces of the singlecrystal silicon donor wafer, and a central plane of the single crystalsilicon donor wafer between the front and back surfaces of the singlecrystal silicon donor wafer, wherein the single crystal silicon donorwafer comprises a cleave plane.

Other objects and features of this invention will be in part apparentand in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of a silicon-on-insulator wafer according to theprior art in which an N-type inversion layer has formed at the interfaceof a buried oxide layer and a P-type handle substrate.

FIG. 2 is a depiction of a silicon-on-insulator wafer according to theprior art comprising a trap rich layer between a high resistivitysubstrate and a buried oxide layer.

FIG. 3 is a depiction of a silicon-on-insulator wafer according to thepresent invention in which no N-type inversion layer is formed at theinterface of the buried oxide layer and the handle substrate.

FIG. 4 is a graph depicting the energy-band diagram of a handle waferaccording to the prior art before BOX formation.

FIG. 5 is a graph depicting the energy-band diagram of a handle waferaccording to the prior art after BOX formation.

FIG. 6 is a graph depicting the energy-band diagram of a handle waferaccording to the present invention before BOX formation.

FIG. 7 is a graph depicting the energy-band diagram of a handle waferaccording to the present invention after BOX formation.

DETAILED DESCRIPTION OF THE EMBODIMENT(S) OF THE INVENTION

According to the present invention, a method is provided for designingand manufacturing semiconductor-on-insulator wafers comprising a singlecrystal semiconductor handle structure, a dielectric layer (commonly aburied oxide layer, or BOX), and a device layer. The single crystalsemiconductor handle structure, e.g., a single crystal semiconductorhandle wafer, is prepared to comprise an intermediate semiconductorlayer having lower electron affinity than the handle substrate. Thisintermediate semiconductor layer is prepared at or near the interface ofthe buried oxide layer and the handle substrate. The single crystalsemiconductor handle structure comprising the intermediate semiconductorlayer of low electron affinity is useful in the production of asemiconductor-on-insulator (e.g., silicon-on-insulator) structure.According to the present invention, the intermediate semiconductor layerof low electron affinity in the single crystal semiconductor handlestructure, e.g., a wafer, is formed at the region at or near theinterface between the buried oxide layer and the handle substrate.Advantageously, the method of the present invention provides aintermediate semiconductor layer of low electron affinity effective forimproving immunity against charge inversion in the region of thestructure at the interface between the buried oxide layer and the handlesubstrate.

A key factor leading to degradation of high resistivitysemiconductor-on-insulator (HR-SOI, e.g., a high resistivitysilicon-on-insulator) RF device performance is N-type inversion layerson the surface of SOI P-type handle structures at the interface with theburied oxide layer (BOX). An inversion layer is induced to neutralizethe positive charge in the BOX that is typically inevitable for oxideson silicon and other semiconductors. See FIG. 1, which is a depiction ofa conventional silicon-on-insulator wafer 1 in which an N-type inversionlayer 10 has formed at the interface of a buried oxide layer 4 and aP-type handle substrate 2. The present invention provides a method ofmanufacturing a high resistivity semiconductor-on-insulator structure,e.g., a high resistivity silicon-on-insulator structure, for use in anRF device, prepared with an improved immunity against inversion of aregion of the handle substrates at or near the interface with the buriedoxide layer. The HR-SOI structure of the present invention is preparedwith a handle structure that comprises an intermediate semiconductorlayer in between of the handle substrate and BOX. The intermediatesemiconductor layer is made of a semiconductor material with an electronaffinity lower than that of the handle substrate (electron affinity isthe energy required to release an electron from the bottom of conductionband to the vacuum level). See FIG. 3, which is a depiction of asilicon-on-insulator structure 30 comprising a handle substrate 32, aburied oxide layer 34 comprising positive charge 36, and a silicondevice layer 38, according to the present invention in which no N-typeinversion layer is formed at the interface of the buried oxide layer andthe handle substrate. Instead, the silicon-on-insulator structure 30comprises an uninverted intermediate semiconductor layer 40 of lowerelectron affinity than the handle substrate. This intermediatesemiconductor layer 40 of lower electron affinity than the handlesubstrate is capable of inhibiting the formation of the N-type inversionlayer.

The reason for the formation of an N-type inversion layer in aconventional P-type handle substrate is illustrated by the energy-banddiagrams provided in FIGS. 4 and 5. FIG. 4 is a graph depicting theenergy-band diagram of a typical P-type handle wafer prior to formationof the BOX, while FIG. 5 is a graph depicting the energy-band diagram ofa handle wafer according to the prior art after BOX formation. Asdepicted in FIG. 4, the conduction band and valence band are typical ofa conventional P-type silicon wafer in a vacuum. After deposition of asilicon oxide layer, the positive charge, which is generally inherentlypresent, therein needs to be neutralized by negative charge. Therefore,any electron carriers (negatively charged) in the substrate will beattracted to the BOX interface and will accumulate there. Accordingly,the interface layer of the substrate will be filled with electrons asopposed to the bulk portion on the P-type substrate. As depicted in FIG.5, the positive charge in BOX causes the bending of the valence band andconduction band of the silicon at the surface with the BOX. Accordingly,negative charges of mobile minority carriers—electrons—emerge at thesurface. They form an interface conductive layer that is called aninversion layer.

According to the method of the present invention, a single crystalsemiconductor handle structure is formed with an intermediatesemiconductor layer at or near the interface of the buried oxide layerand the handle substrate. The intermediate semiconductor layer has lowerelectron affinity than the handle substrate. The intermediatesemiconductor layer improves the handle structure's ability to resistformation of an N-type inversion layer near the BOX interface. Theintermediate semiconductor layer is engineered to have higher electronenergy than the handle substrate, which is typically a P-type substrate.By forming a higher electron energy semiconductor layer at or near theinterface of the handle substrate and the BOX, the attraction ofelectrons, that is, mobile negative charge, from the high resistivitysubstrate to the BOX interface is decreased. Stated another way, thepositive charge in the BOX will be neutralized by essentially immobile(or much less mobile) negatively charged ions in the intermediatesemiconductor layer. For example, if the intermediate semiconductorlayer comprises a SiGe layer, the immobile charge neutralized atomscomprise Si⁻ or Ge⁻ ions in the SiGe crystal network. The mechanism ofthe inversion inhibiting effect of the semiconductor layer in the handlesubstrate of the present invention is illustrated in FIGS. 6 and 7. FIG.6 is a graph depicting the energy-band diagram of a handle waferaccording to the present invention before BOX formation, which depictsthe enhanced P-type nature of the intermediate semiconductor layer, asshown by the relative positions of the conduction band and the valenceband compared to the Fermi level. FIG. 7 is a graph depicting theenergy-band diagram of a handle wafer according to the present inventionafter BOX formation. The intermediate semiconductor layer alters thevalence band and conduction band such that, even after BOX formation,these bands effectively retain their P-type character, even in the nearBOX depletion layer (E_(c)−E_(f)>E_(f)−E_(y)).

With reference to FIG. 3, the substrate for use in the present inventionis a single crystal semiconductor handle substrate 32, e.g., a singlecrystal semiconductor handle wafer. In general, the single crystalsemiconductor handle substrate 32 comprises two major, generallyparallel surfaces. One of the parallel surfaces is a front surface ofthe substrate 32, and the other parallel surface is a back surface ofthe substrate 32. The substrate 32 comprises a circumferential edgejoining the front and back surfaces, and a central plane between thefront and back surfaces. The substrate 32 additionally comprises animaginary central axis perpendicular to the central plane and a radiallength that extends from the central axis to the circumferential edge.In addition, because semiconductor substrates, e.g., silicon wafers,typically have some total thickness variation (TTV), warp, and bow, themidpoint between every point on the front surface and every point on theback surface may not precisely fall within a plane. As a practicalmatter, however, the TTV, warp, and bow are typically so slight that toa close approximation the midpoints can be said to fall within animaginary central plane which is approximately equidistant between thefront and back surfaces. According to the method of the presentinvention, in the manufacture of semiconductor-on-insulator structures30, the device layer 38 is generally derived from a single crystalsemiconductor donor substrate (not picture). In some embodiments, thedonor substrate may be substantially identical to the handle substrate32 prior to any of the operations described herein, i.e., comprise thesame material and have the same general dimensions. In some embodiments,the handle substrate 32 and the donor substrate may comprise a differentmaterial, e.g., in the formation of a sapphire-on-insulator structure.

Prior to any operation as described herein, the front surface and theback surface of the handle substrate 32 (and a donor substrate) may besubstantially identical. A surface is referred to as a “front surface”or a “back surface” merely for convenience and generally to distinguishthe surface upon which the operations of method of the present inventionare performed. In the context of the present invention, a “frontsurface” of a single crystal semiconductor handle substrate 32, e.g., asingle crystal silicon handle wafer, refers to the major surface of thesubstrate that becomes an interior surface of the bonded structure 30.According to the method of the present invention, the intermediatesemiconductor layer 40 is prepared on the front surface of the singlecrystal semiconductor handle substrate 32. Accordingly, a “back surface”of a single crystal semiconductor handle substrate 32, e.g., a handlewafer, refers to the major surface that becomes an exterior surface ofthe bonded structure. Similarly, a “front surface” of a single crystalsemiconductor donor substrate, e.g., a single crystal silicon donorwafer, refers to the major surface of the single crystal semiconductordonor substrate that becomes an interior surface of the bondedstructure, and a “back surface” of a single crystal semiconductor donorsubstrate, e.g., a single crystal silicon donor wafer, refers to themajor surface that becomes an exterior surface of the bonded structure.The front surface of the donor substrate may comprise a dielectriclayer, e.g., an oxide layer, which becomes an interior dielectric layer34 in the final semiconductor-on-insulator structure 30.

The single crystal semiconductor handle substrate and the single crystalsemiconductor donor substrate may be single crystal semiconductorwafers. In preferred embodiments, the semiconductor wafers comprise asemiconductor material selected from the group consisting of silicon,silicon carbide, sapphire, aluminum nitride, silicon germanium, galliumarsenide, gallium nitride, indium phosphide, indium gallium arsenide,germanium, and combinations thereof. The handle substrate 32 and thedevice layer 38 may comprise the same semiconductor material, or theymay be different. In view thereof, SOI structures 30 may comprise, e.g.,silicon-on-insulator, sapphire-on-insulator, aluminumnitride-on-insulator, and other combinations. The single crystalsemiconductor wafers, e.g., the single crystal silicon handle wafer andsingle crystal silicon donor wafer, of the present invention typicallyhave a nominal diameter of at least about 150 mm, at least about 200 mm,at least about 250 mm, at least about 300 mm, at least about 400 mm, atleast about 450 mm, or more. Wafer thicknesses may vary from about 250micrometers to about 1500 micrometers, suitably within the range ofabout 500 micrometers to about 1000 micrometers.

In particularly preferred embodiments, the single crystal semiconductorwafers comprise single crystal silicon wafers which have been slicedfrom a single crystal ingot grown in accordance with conventionalCzochralski crystal growing methods or float zone growing methods. Suchmethods, as well as standard silicon slicing, lapping, etching, andpolishing techniques are disclosed, for example, in F. Shimura,Semiconductor Silicon Crystal Technology, Academic Press, 1989, andSilicon Chemical Etching, (J. Grabmaier ed.) Springer-Verlag, N.Y., 1982(incorporated herein by reference). Preferably, the wafers are polishedand cleaned by standard methods known to those skilled in the art. See,for example, W. C. O'Mara et al., Handbook of Semiconductor SiliconTechnology, Noyes Publications. If desired, the wafers can be cleaned,for example, in a standard SC1/SC2 solutions. In some embodiments, thesingle crystal silicon wafers of the present invention are singlecrystal silicon wafers which have been sliced from a single crystalingot grown in accordance with conventional Czochralski (“Cz”) crystalgrowing methods, typically having a nominal diameter of at least about150 mm, at least about 200 mm, at least about 250 mm, at least about 300mm, at least about 400 mm, at least about 450 mm, or more. Preferably,both the single crystal silicone handle wafer and the single crystalsilicone donor wafer have mirror-polished front surface finishes thatare free from surface defects, such as scratches, large particles, etc.Wafer thickness may vary from about 250 micrometers to about 1500micrometers, suitably within the range of about 500 micrometers to about1000 micrometers. In some specific embodiments, the wafer thickness maybe about 725 micrometers.

In some embodiments, the single crystal semiconductor wafers, i.e.,handle wafer and donor wafer, comprise interstitial oxygen inconcentrations that are generally achieved by the Czochralski-growthmethod. In some embodiments, the semiconductor wafers comprise oxygen ina concentration between about 1 PPMA and about 30 PPMA, such as betweenabout 4 PPMA and about 18 PPMA. In some embodiments, the semiconductorwafers comprise oxygen in a concentration between about 10 PPMA andabout 35 PPMA. Interstitial oxygen may be measured according to SEMI MF1188-1105.

In some embodiments, the semiconductor handle substrate, e.g., a singlecrystal semiconductor handle substrate, such as a single crystal siliconhandle wafer, has a relatively high minimum bulk resistivity. Highresistivity wafers are generally sliced from single crystal ingots grownby the Czochralski method or float zone method. Cz-grown silicon wafersmay be subjected to a thermal anneal at a temperature ranging from about600° C. to about 1000° C. in order to annihilate thermal donors causedby oxygen that are incorporated during crystal growth. In someembodiments, the single crystal semiconductor handle wafer has a minimumbulk resistivity of at least 50 Ohm-cm, such as between about 50 Ohm-cmand about 100,000 Ohm-cm, between about 100 Ohm-cm and about 100,000Ohm-cm, or between about 500 Ohm-cm and about 10,000 Ohm-cm, or betweenabout 750 Ohm-cm and about 10,000 Ohm-cm, between about 1000 Ohm-cm andabout 10,000 Ohm-cm, between about 2000 Ohm-cm and about 10,000 Ohm-cm,or between about 3000 Ohm cm and about 5,000 Ohm-cm. In someembodiments, the single crystal semiconductor handle wafer has a minimumbulk resistivity between about 750 Ohm-cm and about 5,000 Ohm-cm.

In preferred embodiments, the high resistivity single crystalsemiconductor handle wafer comprises a P-type dopant, typically boron.In general, the concentration of the P-type dopant is on the order of1×10¹⁴/cm³ or less, such as 1×10¹³/cm³ or less, or 1×10¹²/cm³ or less.In some embodiments, the concentration of the P-type dopant may bebetween about 1×10¹²/cm³ and about 1×10¹³/cm³. Methods for preparinghigh resistivity wafers are known in the art, and such high resistivitywafers may be obtained from commercial suppliers, such as SunEdison,Inc. (St. Peters, Mo.; formerly MEMC Electronic Materials, Inc.).

According to the method of the present invention, semiconductor materialis deposited as an intermediate semiconductor layer onto the exposedfront surface of the single crystal semiconductor handle substrate,e.g., a single crystal silicon handle wafer. In some embodiments, thefront surface of the single crystal semiconductor handle substratecomprises an exposed oxidized front surface layer. The intermediatesemiconductor layer may comprise a polycrystalline structure, anamorphous structure, a nanocrystalline structure, or a monocrystallinestructure. Monocrystalline materials are typically deposited byprocesses that cause the semiconductor material to retain the crystalstructure of the underlying substrate, such as epitaxial deposition. Ananocrystalline material includes a material with very small grain sizesof the order of less than about 100 nm. To describe a structure asnanocrystalline refers to a transitional structure from polycrystallineto amorphous. A polycrystalline material denotes a material comprisingsmall crystals having random crystal orientations. Polycrystallinematerial grains may be as small in size as about 20 nanometers.Amorphous materials lack short range and long range order. In someinstance, the material may comprise grains having crystallinity of nomore than about 10 nanometers while still be considered essentiallyamorphous.

The intermediate semiconductor layer formed at or near the interface ofthe BOX and the handle substrate comprises a material of lower electronaffinity relative to the single crystal semiconductor handle substrate.Exemplary materials of lower electron affinity than the single crystalsemiconductor handle substrate, typically a single crystal siliconhandle substrate, include silicon doped with one of germanium, carbon,tin, and combinations thereof, or germanium doped with tin. For example,the material may be selected from the group consisting ofSi_(1-x)Ge_(x), Si_(1-x)C_(x), Si_(1-x-y)Ge_(x)Sn_(y),Si_(1-x-y-z)Ge_(x)Sn_(y)C_(z), Ge_(1-x)Sn_(x), and any combinationthereof. In these chemical formulas, x, y, and z are molar ratiosvarying in value from 0 to 1, such that the material is a compoundsemiconductor. In some embodiments, 0<x<1, and preferably, 0.01<x<0.99,or 0.1<x<0.9, or 0.2<x<0.7. In other embodiments, 0<x+y<1, andpreferably 0.01<x+y<0.99, or 0.1<x+y<0.9, or 0.2<x+y<0.7. In still otherembodiments, 0<x+y+z<1, and preferably 0.01<x+y+z<0.99, or0.1<x+y+z<0.9, or 0.2<x+y+z<0.7. In some embodiments, the values of x,y, and z vary between 0.01 and 0.99, such as between about 0.05 andabout 0.95, or between about 0.1 and about 0.9. Preferably, the valuesfor x, y, and z may be between about 0.2 and about 0.7. Additionalsemiconductor materials include group IIIA-nitrides and semiconductoroxides. In some embodiments, the group IIIA-nitrides may include GaN,AlN, InN, BN, and Al_(1-x-y-z)Ga_(x)In_(y)B_(z)N with 0<x+y+z<1, morepreferably 0.01<x+y+z<0.99, or between 0.1<x+y+z<0.9. In someembodiments, the values of x, y, and z may be between about 0.2 andabout 0.7. Semiconductor oxides include SnO₂, TiO₂, ZnO.

The material for deposition onto the front surface of the single crystalsemiconductor handle substrate, e.g., an optionally oxidized frontsurface of a single crystal silicon wafer, may be deposited by meansknown in the art. The formation of the layer can be accomplished withchemical vapor phase deposition (CVD), metalorganic CVD, molecular beamepitaxy (MBE), plasma enhanced CVD, atomic layer deposition, physicalvapor deposition, pulsed laser deposition, implantation in Si, or layertransfer. In some embodiments, the semiconductor material may bedeposited using low pressure chemical vapor deposition (LPCVD), plasmaenhanced chemical vapor deposition (PECVD), or physical vapor deposition(PVD). For example, polycrystalline silicon doped with germanium,carbon, tin, and combinations thereof may be deposited by chemical vapordeposition. In some embodiments, silicon deposition may occur in a CVDreactor using dichlorosilane as the precursors for the Si. Alternativesilicon precursors may include, but are not limited to, silane,disilane, trichlorosilane, trisilane, pentasilane, neopentasilane orother higher order precursors. In some embodiments, silicon may bedeposited onto the surface oxidation layer by pyrolyzing a siliconprecursor, such as silane (SiH₄), in a temperature range between about350° C. and about 950° C., or between about 450° C. and about 950° C.,or between about 550° C. and about 690° C., such as between about 580°C. and about 650° C. The chamber pressure may range from about 70 toabout 400 mTorr. For some deposition processes, the pressure may rangefrom about 0.5 to about 750 Torr, such as between about 1 and about 750Torr, or between about 1 and about 60 Torr. The semiconductor layerdeposition rate may range from 10-500 nm/min, preferably 20-100 nm/min.Silicon may be doped with germanium by including a germanium compound inthe dopant gas, such as organogermanium compounds, such as germane,digermane, isobutylgermane, alkylgermanium trichlorides, anddimethylaminogermanium trichloride. Additionally, custom precursors suchas germlysilane or silylgermane could be used for the deposition of theSiGe layer. Organometallic Tin compounds, such as Tin chloride, and Tinhydride precursors are typically used for Tin containing compounddeposition. Silicon doped with carbon may be deposited by thermal plasmachemical vapor deposition in epitaxial reactors using precursors such assilicon tetrachloride and methane. Suitable carbon precursors for CVD orPECVD include methylsilane, methane, ethane, ethylene, among others. ForLPCVD deposition, methylsilane is a particularly preferred precursorsince it provides both carbon and silicon. For PECVD deposition, thepreferred precursors include silane and methane.

Silicon doped with C, Ge, or Sn may be deposited in a manner such thatthe concentration of the dopant C, Ge, or Sn changes, and generallygradually increases, in the direction of deposition from the singlecrystal semiconductor handle substrate. The concentration may varyaccording to a linear gradient, a parabolic gradient, or may be variedin a stepwise manner. For example, in a process in which the Ge contentis increased in a stepwise fashion, a first layer of 50 nm thickSi_(1-x)Ge_(x) with x=0.2 is deposited followed by a secondSi_(1-x)Ge_(x) layer of 30 nm with x=0.4. Then a third layer of 30 nmthick Si_(1-x)Ge_(x) with x=0.6 is deposited. The additional benefit ofthe graded Si_(1-x)Ge_(x) layer structure is that an electric field isbuilt up in the Si_(1-x)Ge_(x) layer stack that pushes the electronsaway from the layer surface. Yet another method to achieve this gradedGe profile is to linearly or parabolically grade the Ge composition froma starting Ge concentration at the handle substrate surface up to afinal Ge concentration that is higher than the starting Ge concentrationover a specified thickness. For example, the deposition ofSi_(1-x)Ge_(x) may begin with suitable precursors in suitable molarratios such that x=0.2, i.e., the initial deposition is ofSi_(0.8)Ge_(0.2), and the germanium precursor concentration may begradually increased until an intermediate layer having thickness betweenabout 0.3 micrometers and about 5 micrometers is formed in which thefinal semiconductor material comprises Si_(0.4)Ge_(0.6). Many othervariations are possible while still falling within the scope of thepresent invention.

Amorphous silicon may be deposited from silicon precursors, such assilane, disilane, dichlorosilane, trichlorosilane, trisilane,pentasilane, neopentasilane or other higher order precursors by plasmaenhanced chemical vapor deposition (PECVD) at temperatures generallyranging between about 75° C. and about 300° C.

Germanium layers, which may optionally be doped with tin, may bedeposited at temperatures up to about 300° C. by chemical vapordeposition by including organogermanium compounds, such as germane,digermane, isobutylgermane, alkylgermanium trichlorides, anddimethylaminogermanium trichloride. Epitaxial deposition is suitable fordepositing a semiconductor layer that essentially retains themonocrystalline structure of the underlying handle substrate. However,depending on deposition conditions, a semiconductor layer depositedusing epitaxial reactor may be deposited as polycrystalline oramorphous. Finally, it is also possible to deposit an epitaxialsemiconductor layer and subject the epitaxially deposited semiconductorlayer to further processing to thereby convert it to highly defectivestructure, similar in properties to polycrystalline material.

In the context of the present invention, Group IIIA refers to the borongroup of elements, including boron, aluminum, gallium, indium.Accordingly, Group IIIA-nitrides include boron nitride, aluminumnitride, gallium nitride, and indium nitride. The Group IIIA-nitridelayer may be deposited using metalorganic chemical vapor deposition(MOCVD), metalorganic vapor phase epitaxy (MOVPE), or molecular beamepitaxy (MBE). In some preferred embodiments, the Group IIIA nitridelayer may be deposited using metalorganic chemical vapor deposition(MOCVD). A suitable MOCVD reactor may be a Veeco TurboDisc or an AixtronG5. In MOCVD, metalorganic compounds are used as the precursors.Aluminum precursors suitable for MOCVD include trimethylaluminum andtriethylaluminum. Gallium precursors for MOCVD include trimethylgalliumand triethylgallium, indium precursors suitable for MOCVD includetrimethylindium, triethylindium, di-isopropylmethylindium, andethyldimethylindium. Nitrogen precursors suitable for MOCVD includeAmmonium, phenyl hydrazine, dimethyl hydrazine, tertiary butyl amine,and ammonia. Boron precursors include diborane, boron chloride,1,3,5-tri(N-methyl)borazine. The molar ratio of Group V precursor (e.g.,ammonia) to Group IIIA precursor (e.g., trimethyl gallium) may bebetween 0.1 to 10000, such as between 1 and 10000, preferably between100 to 1000. The deposition temperature ranges from 700° C. to 1200° C.,depending on the composition of the alloy. In-containing nitridesrequire a deposition temperature towards the lower end, between 700 and800° C. The Group IIIA nitride may be formed under reduced pressure,such as between about 10 Torr to about 760 Torr (about 101 kPa),preferably between about 10 Torr (about 1.33 kPa) and about 80 Torr(about 10.67 kPa). Al-rich nitrides prefers a deposition pressure on thelow side, 10-80 Torr. Nitrogen, hydrogen or the mixture of nitrogen andhydrogen can be used as the carrier gas. Nitrogen carrier gas ispreferred when In-containing nitride is deposited. The thickness of thenitride alloys ranges from 0.01 to 1 μm, preferably from 0.1 to 0.5 μm.In MBE, either metalorganic precursors or solid sources of Ga, In, Al, Bcan be used. N₂ or NH₃ can be used to as the nitride precursor. Plasmacan be used to crack the precursors and lower the growth temperatures.Deposition temperature ranges from 400° C. to 900° C., preferablybetween 600° C. and 800° C. MBE operates in ultrahigh vacuum (10⁻¹⁰-10⁻⁸Torr). The thickness of the nitride alloys ranges from 0.01 to 1 μm,preferably from 0.1 to 0.5 μm.

Deposition of SnO₂, TiO₂ and ZnO₂ is carried out in a chemical vaporphase deposition chamber. The typical Tin metalorganic precursorsinclude but not limited to tetramethyltin, trimethyltinchloride. Thetypical Titanium metalorganic precursors include but not limited tomethyltitaniumchloride and titaniumchloride; the typical Zn metalorganicprecursors include but not limited to Dimethylzinc and Diethylzinc.Oxygen, Ozone, or water is used as the oxygen source. Deposition iscarried out from 400° C. to 600° C. with reactor pressure rangingbetween about 10 Torr to about 760 Torr (about 101 kPa), preferablybetween about 10 Torr (about 1.33 kPa) and about 80 Torr (about 10.67kPa).

According to some embodiments, the intermediate semiconductor layerformed on the front surface layer of the single crystal semiconductorhandle wafer may be deposited as a strained semiconductor layer. Ingeneral, an epitaxially deposited layer essentially retains thecrystalline form of the underlying substrate, which may be (100), (110),or (111). In instances wherein the lattice constants of thesemiconductor layer and the substrate are different, the epitaxial layerbecomes strained to accommodate the difference, as is often the case forSiGe and Si:C materials grown on top of silicon. In some embodiments, itmay be desirable to retain the strained character of the depositedintermediate semiconductor layer. In some embodiments, however, themethod of the present invention further includes partially relaxing orfully relaxing the semiconductor layer. During post-epitaxial waferprocessing, such as high-temperature anneals, due to high strain, thestress-induced defects, such as dislocations, may generate and multiplyin the epitaxial layer. The development of such defective structuresreduces in internal stresses in the layer and relaxes the strainedlayer. This relaxation may be partial or may fully relax thesemiconductor layer. It may be possible during epitaxial deposition thatthe epi layer reaches a critical thickness in which relaxation mayoccur. In some embodiments, the strained epi layer may become fullyrelaxed due to the developed defective structure. Typically, the higherthe temperature and longer the duration of post-epi thermal treatments,the higher the probability for the full relaxation. As an example, aSi_(0.5)Ge_(0.5) layer grown by epitaxial deposition on a silicon handlestructure will be essentially relaxed during 1 hour anneals attemperatures greater than 1000° C.

The layer thickness of the intermediate semiconductor layer isdetermined experimentally such that it is sufficient to meet the devicerequirements but not extended too much as the latter increases themanufacturing cost. The overall thickness of the intermediatesemiconductor layer may be between about 0.3 micrometers and about 5micrometers, such as between about 0.3 micrometers and about 3micrometers, such as between about 0.3 micrometers and about 2micrometers or between about 2 micrometers and about 3 micrometers.

According to the present invention, the role of the intermediatesemiconductor layer of lower electron affinity than the handle substrateis not necessarily charge trapping. However, this intermediatesemiconductor layer may also trap charges, which brings with it thatextra benefit in RF performance. In some embodiments, the method of thepresent invention may be used in combination with conventional chargetrapping layers. In some embodiments, the CTL may be placed under theBOX, i.e., the charge trapping layer is between the intermediatesemiconductor layer and the dielectric layer. In some embodiments, theCTL may be under the intermediate semiconductor layer of the presentinvention, i.e., the charge trapping layer is between the intermediatesemiconductor layer and the handle substrate.

The intermediate semiconductor layer may be further treated byconventional methods of semiconductor processing to modify itsproperties in a desired way. For example, a SiGe layer may be implantedwith boron that stabilizes the SiGe crystal structure during hightemperature treatments. An implantation with heavy ions such as Argonmay be used to amorphize the semiconductor layer adding charge trappingability. Plasma or wet chemical etching on top of the semiconductorlayer may improve its bonding properties essential for high quality SOIfabrication. An epitaxial growth may yield the semiconductor layer tohave rough surface. In some embodiments, therefore, chemical mechanicalpolishing may be required for ensure the surface smoothness during SOIbonding.

After deposition of the intermediate semiconductor layer, an oxide filmis formed on top of the deposited semiconductor material film. This maybe accomplished by means known in the art, such as thermal oxidation (inwhich some portion of the deposited semiconductor material film will beconsumed) and/or CVD oxide deposition. The oxide can be a chemicaloxide, thermal oxide or deposited oxide. A preferred oxide thickness canbe in the range of 5 Å-10000 Å, but more preferably in the range of 5Å-50 Å. As previously mentioned, an oxide film, e.g., silicon oxide,generally, in many cases inherently, comprises a net positive charge.The positive charge in the semiconductor layer results from severaloxide charges. The charges include interface-trapped charge Q_(it),which is due to the interfacial properties between the buried oxide,e.g., silicon oxide, and the single crystal semiconductor handlematerial, e.g., single crystal silicon. This charge is dependent on thechemical composition of the interface. The interface trap charge densityis orientation dependent. For example, the positive charge density inthe near surface region of a single crystal silicon handle substratehaving <100> crystal orientation is about an order of magnitude smallerthan the charge density in silicon having <111> crystal orientation.After a 450° C. hydrogen anneal, the interface-trapped charge <100>crystal orientation silicon may be as low as 10¹⁰/cm². An additionalsource of positive charge is the fixed-oxide charge, Q_(f), which is thecharge that most affects HR-SOI performance. The fixed-oxide charge islocated within approximately 3 nm from the SiO₂—Si interface. Thischarge is fixed and cannot be charged or discharged over a widevariation of surface potential. Generally, Q_(f) is positive and dependson oxidation and annealing conditions and on silicon orientation. It hasbeen suggested that when the oxidation is stopped, some ionic silicon isleft near the interface, which may result in the positive interfacecharge Q_(f). Typical fixed-oxide charge densities for a carefullytreated SiO₂—Si interface system are about 10¹⁰/cm² for a <100> crystalorientation surface and about 5×10¹⁰/cm² for a <111> crystal orientationsurface. Another source of positive charge comprises oxide-trappedcharge Q_(ot). Oxide-trapped charges are associated with defects in thesilicon dioxide. These charges can be created, for example, by X-rayradiation or high-energy electron bombardment the trap are distributedinside the oxide layer. Most of process-related oxide trapped charge canbe removed by low-temperature annealing. Finally, the positive oxidecharges may comprise mobile ionic charges, Q_(m). The mobile ioniccharges Q_(m), such as sodium or other alkali ion are positive andmobile within the oxide under raised temperature (e.g. >100° C.) andhigh electric field operation. These sources of positive charge in theburied oxide layer are associated with HR-SOI device degradation due tothe formation of the N-type inversion layer, as previously described.The intermediate semiconductor layer of the present invention comprisinglow electron affinity material enables the P-type handle substrate toretain its P-type character even in the interface region near the BOX.

After oxidation, wafer cleaning is optional. If desired, the wafers canbe cleaned, for example, in a standard SC1/SC2 solution. Additionally,the wafers may be subjected to chemical mechanical polishing (CMP) toreduce the surface roughness, preferably to the level of RMS_(2×2 um2)is less than about 5 angstroms, wherein root mean squared—

${R_{q} = \sqrt{\frac{1}{n}{\sum\limits_{i = 1}^{n}y_{i}^{2}}}},$the roughness profile contains ordered, equally spaced points along thetrace, and y_(i) is the vertical distance from the mean line to the datapoint.

The single crystal semiconductor handle wafer prepared according to themethod described herein to comprise a single crystal semiconductorhandle substrate, an intermediate semiconductor layer of lower electronaffinity than the handle substrate, and an oxide layer is next bonded asingle crystal semiconductor donor substrate, e.g., a single crystalsemiconductor donor wafer, which is prepared according to conventionallayer transfer methods. That is, the single crystal semiconductor donorwafer may be subjected to standard process steps including oxidation,implant, and post implant cleaning. Accordingly, a single crystalsemiconductor donor substrate, such as a single crystal semiconductorwafer of a material that is conventionally used in preparation ofmultilayer semiconductor structures, e.g., a single crystal silicondonor wafer, that has been etched and polished and optionally oxidized,is subjected to ion implantation to form a damage layer in the donorsubstrate. Ion implantation may be carried out in a commerciallyavailable instrument, such as an Applied Materials Quantum II. Implantedions include He, H, H₂, or combinations thereof. In some embodiments itmay be desirable to subject the single crystal semiconductor donorwafers, e.g., single crystal silicon donor wafers, to a clean after theimplant. In some preferred embodiments, the clean could include aPiranha clean followed by a DI water rinse and SC1/SC2 cleans. In someembodiments of the present invention, the single crystal semiconductordonor substrate having a damage layer therein formed by helium ionand/or hydrogen ion implant is annealed at a temperature sufficient toform a thermally activated cleave plane in the single crystalsemiconductor donor substrate. An example of a suitable tool might be asimple Box furnace, such as a Blue M model. In some preferredembodiments, the ion implanted single crystal semiconductor donorsubstrate is annealed at a temperature of from about 200° C. to about350° C., from about 225° C. to about 325° C., preferably about 300° C.Thermal annealing may occur for a duration of from about 2 hours toabout 10 hour, preferably a duration of about 8 hours. Thermal annealingwithin these temperatures ranges is sufficient to form a thermallyactivated cleave plane. After the thermal anneal to activate the cleaveplane, the single crystal semiconductor donor substrate surface ispreferably cleaned.

In some embodiments, the cleaned single crystal semiconductor donorsubstrate having the thermally activated cleave plane therein issubjected to oxygen plasma and/or nitrogen plasma surface activation. Insome embodiments, the oxygen plasma surface activation tool is acommercially available tool, such as those available from EV Group, suchas EVG®810LT Low Temp Plasma Activation System. The single crystalsemiconductor donor wafer having the thermally activated cleave plane isloaded into the chamber. The chamber is evacuated and backfilled with O₂to a pressure less than atmospheric to thereby create the plasma. Thesingle crystal semiconductor donor wafer is exposed to this plasma forthe desired time, which may range from about 1 second to about 120seconds. Oxygen plasma surface oxidation is performed in order to renderthe front surface of the single crystal semiconductor donor substratehydrophilic and amenable to bonding to a single crystal semiconductorhandle substrate prepared according to the method described above tohave a nanocavity layer and preferably a silicon oxide layer.

The hydrophilic front surface layer of the single crystal semiconductordonor substrate and the oxidized front surface of the single crystalsemiconductor handle substrate having the nanocavity layer are nextbrought into intimate contact to thereby form a bonded structure. Sincethe mechanical bond is relatively weak, the bonded structure is furtherannealed to solidify the bond between the donor wafer and the carrierwafer. The bonded structure may be annealed at a temperature up to about1200° C., such as between about 1000° C. and about 1200° C., preferablyat a temperature of about 1125° C. The thermal anneal may have aduration between about 30 minutes hours and about 8 hours, preferablyfor about 4 hours.

After the thermal anneal, the bond between the single crystalsemiconductor donor substrate and the single crystal semiconductorhandle substrate is strong enough to initiate layer transfer viacleaving the bonded structure at the cleave plane. Cleaving may occuraccording to techniques known in the art. In some embodiments, thebonded structure may be placed in a conventional cleave station affixedto stationary suction cups on one side and affixed by additional suctioncups on a hinged arm on the other side. A crack is initiated near thesuction cup attachment and the movable arm pivots about the hingecleaving the wafer apart.

After the high temperature anneal and cleave, the bonded structure maybe subjected to a cleaning process designed to remove thin thermal oxideand clean particulates from the surface. In some embodiments, the singlecrystal semiconductor donor wafer may be brought to the desiredthickness and smoothness by subjecting to a vapor phase HCl etch processin a horizontal flow single wafer epitaxial reactor using H₂ as acarrier gas. In some embodiments, an epitaxial layer may be deposited onthe transferred device layer. The finished SOI wafer may then besubjected to end of line metrology inspections and cleaned a final timeusing typical SC1-SC2 process.

According to the present invention and with reference to FIG. 3, asemiconductor-on-insulator structure 30 is obtained with an intermediatesemiconductor layer 40 embedded underneath a dielectric layer 34 (e.g.,a BOX) and in contact with the handle substrate 32. The intermediatesemiconductor layer 40 comprises a semiconductor material having lowerelectron affinity than the single crystal semiconductor handle substrate32. The intermediate semiconductor layer 40 in asemiconductor-on-insulator structure 30 under the dielectric layer 34can be effective for resisting formation of an N-type inversion layer inthe region near the BOX, thereby preserving the P-type electricalcharacter of the high resistivity substrate 32.

Having described the invention in detail, it will be apparent thatmodifications and variations are possible without departing from thescope of the invention defined in the appended claims.

The following non-limiting examples further illustrate the presentinvention.

Example 1

200 mm single side polished single crystal silicon wafers withresistivity >750 Ohm-cm (SunEdison, Inc.; St. Peters, Mo.) are coatedwith SiGe. A layer of Si_(1-x)Ge_(x) is epitaxially deposited on theHR—Si handle substrate. The composition of Ge ranges from 0 to 100%. Thethickness of the Si_(1-x)Ge_(x) layer is from 10-2000 nm, preferably50-500 nm. The deposition is carried out in a CVD reactor usingdichlorosilane and germane as the precursors for the Si and Gerespectively. The deposition temperature ranges from 450° C. to 950° C.at a pressure of 1-750 Torr, preferably 1-60 Torr. A deposition rate of10-500 nm/min, preferably 20-100 nm/min, is used. The resulting surfaceroughness (measured with AFM Rms) is ideally from 1 Å-10 Å and CMP canbe used to planarize the surface if a higher surface roughness isobtained after the epitaxial deposition. The threading dislocationdensity ranges from 0 to 10¹⁰ cm⁻². Both the threading dislocations andthe misfit dislocations have dangling bonds that act as carrier traps.Additional traps can be created by deep level metal gettering due to thestrain field associated with the dislocations.

Example 2

200 mm single side polished single crystal silicon wafers withresistivity >750 Ohm-cm (SunEdison, Inc.; St. Peters, Mo.) are coatedwith SiGe. The Si_(1-x)Ge_(x) layer consists of a series ofGe-concentrated graded layers epitaxially grown on the HR-Si handlesubstrates. The Ge concentration gradually increases from the beginningof deposition to the end of deposition by changing the gas phaseconcentration of dichlorosilane and germane in the CVD chamber. Thisgraded Ge profile is to linearly grade the Ge composition from astarting Ge concentration at the handle substrate surface up to a finalGe concentration that is higher than the starting Ge concentration overa specified thickness. CMP process may be required to achieve Rms<5 Å.

Example 3

200 mm single side polished single crystal silicon wafers withresistivity >750 Ohm-cm (SunEdison, Inc.; St. Peters, Mo.) are coatedwith SiGe. The Si_(1-x)Ge_(x) layer consists of a series ofGe-concentrated graded layers epitaxially grown on the HR-Si handlesubstrates. The Ge concentration is changed in a stepped way. A firstlayer of 50 nm thick Si_(1-x)Ge_(x) with x=0.2 is deposited followed bya second Si_(1-x)Ge_(x) layer of 30 nm with x=0.4. Then a third layer of30 nm thick Si_(1-x)Ge_(x) with x=0.6 is deposited. CMP process may berequired to achieve Rms<5 Å.

Example 4

200 mm single side polished single crystal silicon wafers withresistivity >750 Ohm-cm (SunEdison, Inc.; St. Peters, Mo.) are coatedwith amorphous Si. An example of the formation of a charge trap layer bythe deposition of an amorphous Si (alternatively, α-Si:C, α-SiGe, α-Geetc) layer is described herewithin. On top of the handle substrate, anamorphous silicon layer is directly deposited inside a CVD chamber. Thedeposition is carried out using silicon precursors that include, but notlimited to, trisilane, silane, disilane, dichlorosilane, neopentasilane,or other higher order precursors. The deposition temperature ispreferably in the range of 350° C.-550° C. at a pressure in the range of0.5 Torr-750 Torr. In the case of an amorphous alloy of Si, theappropriate alloy precursor gas can be added to the reactor chamber inaddition to the silicon precursor gas (e.g. germane or digermane for anα-SiGe layer, methylsilane for an α-Si:C layer, etc). An alternateapproach to forming the amorphous layer on top of the handle substrateis to insert a thin oxide between the handle and the amorphous layer.The oxide can be a chemical oxide, thermal oxide or deposited oxide. Apreferred oxide thickness can be in the range of 5 Å-10000 Å, but morepreferably in the range of 5 Å-50 Å. The insertion of the thin oxidelayer between the amorphous layer and the handle substrate will minimizethe amount of recrystallization of the amorphous layer during subsequentthermal cycles. The final amorphous layer should have an RMS roughnessin the range of 1 Å-10 Å. Chemical Mechanical Polishing (CMP) can beused to planarize the amorphous silicon surface to achieve the desiredroughness.

Example 5

200 mm silicon wafer with resistivity 3000 Ohm-cm is selected as handlesubstrate for SOI fabrication. 1.5 um epitaxial layer of SiGe is grownin an epitaxial low pressure CVD reactor at 650° C. using source gasesSiH₄ and GeH₄. No special attention is required to control the crystalstructure of the epitaxial layer. The handle substrate is bonded to adonor wafer.

The donor wafer selected is boron doped with resistivity of 10-20Ohm-cm. Before bonding, the donor wafer receives thermal oxidation inwet oxygen at 1000° C. to obtain 0.4 um oxide thickness. Then, ionimplantation of with He⁺ and H₂ ⁺ ions is conducted to the dose of about1×10¹⁶ ions/cm² and energy of 80 keV. Finally, before the bonding thedonor wafer is annealed at 400° C. for 30 minutes.

The handle substrate and the donor wafer are bonded at the surfaces ofthe epitaxial layer and thermal oxide correspondingly. To improve thebonding strength, both surfaces are activated in nitrogen plasma.

The donor wafer is mechanically cleaved by pulling its backside from thehandle substrate fixed on a vacuum chuck. A thin silicon layer and thethermal oxide from the donor wafer are left on the surface of the handlesubstrate. The transferred silicon layer is thinned to a desiredthickness by dry etch in HCl gas at the temperature of about 1050° C. inan epitaxial reactor.

As various changes could be made in the above compositions and processeswithout departing from the scope of the invention, it is intended thatall matter contained in the above description be interpreted asillustrative and not in a limiting sense.

When introducing elements of the present invention or the preferredembodiment(s) thereof, the articles “a,” “an,” “the,” and “said” areintended to mean that there are one or more of the elements. The terms“comprising,” “including,” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

What is claimed is:
 1. A multilayer handle structure comprising, inorder: a single crystal silicon wafer handle substrate comprising twomajor, generally parallel surfaces, one of which is an oxidized frontsurface of the single crystal silicon wafer handle substrate and theother of which is a back surface of the single crystal silicon waferhandle substrate, a circumferential edge joining the oxidized front andback surfaces of the single crystal silicon wafer handle substrate, anda central plane of the single crystal silicon wafer handle substratebetween the oxidized front surface and back surface of the singlecrystal silicon wafer handle substrate, wherein the single crystalsilicon wafer handle substrate comprises a p-type dopant, has <100>crystal orientation and has a bulk resistivity between about 750 ohm-cmand about 100,000 Ohm-cm; a charge trapping layer in interfacial contactwith the oxidized front surface of the single crystal silicon waferhandle substrate, wherein the charge trapping layer is between anintermediate semiconductor layer and the oxidized front surface of thesingle crystal semiconductor handle substrate; intermediatesemiconductor layer having electron affinity lower than that of thesingle crystal silicon wafer handle substrate, wherein the intermediatesemiconductor layer is in interfacial contact with the front surface ofthe charge trapping layer and comprises a polycrystalline, amorphous,nanocrystalline, or monocrystalline structure and comprising a materialselected from the group consisting of a group IIIA-nitride, a metaloxide, and any combination thereof, wherein the group IIIA-nitride isselected from the group consisting of GaN, AlN, InN, BN, andAl_(1-x-y-z)Ga_(x)In_(y)B_(z)N, wherein x, y, and z are molar ratioswith values between 0.1 and 0.9 and further wherein the metal oxide isselected from the group consisting of SnO₂, TiO₂, and ZnO; and asemiconductor oxide layer in interfacial contact with the intermediatesemiconductor layer.
 2. The multilayer structure of claim 1 wherein theintermediate semiconductor layer further comprises implanted boron. 3.The multilayer structure of claim 1 wherein the intermediatesemiconductor layer further comprises implanted argon.
 4. The multilayerhandle structure of claim 1 wherein the single crystal silicon waferhandle substrate comprises a single crystal silicon wafer having <100>crystal orientation and is sliced from a single crystal silicon ingotgrown by the Czochralski method or the float zone method.
 5. Themultilayer handle structure of claim 1 wherein the single crystalsilicon wafer handle substrate has a bulk resistivity between about 1000ohm cm and about 10,000 Ohm-cm.
 6. The multilayer handle structure ofclaim 1 wherein the single crystal silicon wafer handle substrate has abulk resistivity between about 2000 Ohm cm and about 10,000 Ohm-cm. 7.The multilayer handle structure of claim 1 wherein the single crystalsilicon wafer handle substrate has a bulk resistivity between about 3000Ohm cm and about 5,000 Ohm-cm.
 8. The multilayer handle structure ofclaim 1 wherein the intermediate semiconductor layer comprises astrained intermediate semiconductor layer.
 9. The multilayer handlestructure of claim 1 wherein the intermediate semiconductor layercomprises a partially relaxed intermediate semiconductor layer.
 10. Themultilayer handle structure of claim 1 wherein the intermediatesemiconductor layer comprises a fully relaxed intermediate semiconductorlayer.
 11. The multilayer handle structure of claim 1 wherein theintermediate semiconductor layer has a thickness of between about 1nanometer and about 2000 nanometers.
 12. The multilayer handle structureof claim 1 wherein the intermediate semiconductor layer has a thicknessof between about 10 nanometers and about 2000 nanometers.
 13. Themultilayer handle structure of claim 1 wherein the intermediatesemiconductor layer has a thickness of between about 20 nanometers andabout 1000 nanometers.
 14. The multilayer handle structure of claim 1wherein the intermediate semiconductor layer having electron affinitylower than that of the single crystal semiconductor handle substratecomprises the group IIIA-nitride selected from the group consisting ofGaN, AlN, InN, BN, and Al_(1-x-y-z)Ga_(x)In_(y)B_(z)N, wherein x, y, andz are molar ratios with values between 0.1 and 0.9.
 15. The multilayerhandle structure of claim 1 wherein the intermediate semiconductor layerhaving electron affinity lower than that of the single crystalsemiconductor handle substrate comprises the group IIIA-nitride selectedfrom the group consisting of GaN, AlN, InN, BN, andAl_(1-x-y-z)Ga_(x)In_(y)B_(z)N, wherein x, y, and z are molar ratioswith values between 0.2 and 0.7.
 16. The multilayer handle structure ofclaim 1 wherein the intermediate semiconductor layer comprises the metaloxide selected from the group consisting of SnO₂, TiO₂, and ZnO.